Ibuprofen is an anti-inflamatory drug. This activity is based on its ability to inhibit the function of cyclo-oxygenase. It exists in two enantiomeric forms because of an asymmetric center alpha to the carbonyl group. In vitro studies have shown that ibuprofen is only active in the S-form enantiomer; conversion of the inactive R- to the active S-form in vivo has been postulated and supported by in vitro evidence. The study of ibuprofen metabolism has been accomplished mainly in vitro by studying pure compounds, or by sacrificing animals (rats) at certain time intervals after administering the drug and then monitoring the appropriate components, either in the plasma of total blood or by cellular extraction from the liver. The latter method is invasive and time-consuming, and can introduce unwanted errors. The purpose of our study is to verify the configuration conversion process of ibuprofen in vivo and to study its reaction mechanism and kinetics by using whole rats in an NMR imaging instrument. The ibuprofen will be labeled at the C2 position with 13-C and 2-H, and its 13-C NMR spectra variation will be followed from localized regions (preferably the liver) of the rat.